This invention relates to a station-side apparatus. The recent prevalence of the Internet is enhancing the demand for higher-speed network communications. To meet this demand for higher-speed communications, PON (Passive Optical Network) is growing.
The PON is a network system which connects an accommodation station (OLT: Optical Line Terminal) installed in a vendor's station and network units (ONUs: Optical Network Units) installed in user premises; in the PON, the signal in an optical fiber connected to the OLT is split into a plurality of fibers with an optical splitter; the plurality of fibers are connected to the ONUs one by one. When a network is configured with the PON, low cost fiber installation and high-speed communications by employment of optical transmission are attained. For these reasons, the PON is spreading all over the world (refer to WO2013/058179, for example).
Among the techniques utilizing the PON, TDM-PON (Time Division Multiplexing Passive Optical Network) is widely employed, which uses optical signals having different wavelengths in downlink transmission from the OLT to ONUs and uplink transmission from the ONUs to the OLT and further applies time-division multiplexing to the signals depending on the ONU. This TDM-PON is employed in B-PON (Broadband PON), E-PON (Ethernet PON), G-PON (Gigabit-capable PON), 10G-EPON, and XG-PON.
In the TDM-PON, the OLT controls the timing of sending optical signals from ONUs to prevent a conflict among the optical signals from the ONUs in uplink transmission. Specifically, the OLT sends each ONU a control frame to specify a permitted transmission period. Each ONU sends an uplink control signal and uplink data during the period specified by the received control frame.
A candidate of next generation PON is a technique utilizing the WDM/TDM-PON accommodating a plurality of conventional TDM-PONs with a plurality of wavelengths. The WDM/TDM-PON accomplishes a large capacity of communication by utilizing multiple wavelengths.
It is proposed to dynamically change the communication wavelength by using a wavelength-tunable optical transmission reception unit for an ONU in the WDM/TDM-PON in “S. Kimura, “10-Gbit/ s TDM-PON and over-40-Gbit/s WDM/TDM-PON systems with OPEX-effective burst-mode technologies”, OFC2009, OWH-6, Mar. 2009”. Another technique for switching the wavelength of an ONU is disclosed in “T. Yoshida, et. al, “An automatic load-balancing DWBA algorithm considering long-time tuning devices for λ-tunable WDM/TDM-PON”, ECOC2013, We.2.F.5, September 2013”. The technique sends a wavelength switching instruction from an OLT to the ONU and receives a wavelength switching completion notice.